1. Field of the Invention
The present invention relates to a toroidal type continuously variable transmission and, in particular, to a toroidal type continuously variable transmission for use in a vehicle or various industrial machines.
2. Description of the Related Art
Conventionally, as a toroidal type continuously variable transmission, there is known such a structure as shown in FIGS. 1 and 2 (U.S. Pat. No. 5,720,689). Here, FIG. 1 is a side view of a basic structure of a toroidal type continuously variable transmission, showing a maximum decelerating state thereof. FIG. 2, similarly to FIG. 1, is a side view of a basic structure of a toroidal type continuously variable transmission, showing a maximum accelerating state thereof.
In the above-cited related toroidal type continuously variable transmission, an input-side disk 2 serving as a first disk is supported concentrically with an input shaft 1. In addition, there is fixed an output-side disk 4 serving as a second disk to the end portion of an output shaft 3 disposed concentrically with the input shaft 1. In the inside of a casing in which the toroidal type continuously variable transmission is stored, there are disposed a pair of trunnions 6, 6 which are able to swing about their respective pivot shafts 5, 5 respectively disposed at positions along an imaginary plane that is perpendicular to an imaginary line connecting the respective axes of the input and output shafts 1 and 3, and distanced from the intersection of the imaginary plane and imaginary line. This physical relation is hereinafter referred to as "torsional relation".
The pivot shafts 5, 5 are respectively disposed on the outer side surfaces of the two end portions of the trunnions 6, 6. Also, the base end portions of displacement shafts 7, 7 are respectively supported in the central portions of the trunnions 6, 6 and, if the trunnions 6, 6 are swung about the pivot shafts 5, 5 respectively, the inclination angles of the displacement shafts 7, 7 can be adjusted freely. On the peripheries of the two displacement shafts 7, 7 supported on the two trunnions 6, 6, there are supported a plurality of power rollers 8, 8 respectively in such a manner that they can be rotated freely. And, the power rollers 8, 8 are respectively interposed between the two input- and output-side disks 2 and 4.
The input- and output-side disks 2 and 4 respectively include inner surfaces 2a and 4a which are opposed to each other, while the sections of the mutually opposing inner surfaces 2a and 4a are formed as concave surfaces which can be obtained by rotating an arc having the pivot shaft 5 as a center thereof. And, the plurality of power rollers 8 and 8 respectively include peripheral surfaces 8a and 8a which are formed as spherical-shaped convex surfaces, while the peripheral surfaces 8a and 8a of the power rollers 8 and 8 are respectively in contact with the inner surfaces 2a and 4a of the input- and output-side disks 2 and 4.
Between the input shaft 1 and input-side disk 2, there is interposed a pressure device 9 of a loading cam type, while the input-side disk 2 is elastically pressed toward the output-side disk 4 by the pressure device 9. The pressure device 9 is composed of a cam plate 10 rotatable together with the input shaft 1, and a plurality of (for example, four pieces of) rollers 12, 12 which are respectively held by a retainer 11.
On one side surface (in FIGS. 1 and 2, on the left side surface) of the cam plate 10, there is formed a cam surface 13 being a curved surface which extends over the circumferential direction of the cam plate 10; and, on the outer surface (in FIGS. 1 and 2, on the right side surface) of the input-side disk 2, there is also formed a similar cam surface 14. And, the rollers 12, 12 are supported in such a manner that they can be freely rotated about their respective shafts which extend in the radial direction with respect to the center of the input shaft 1.
When the above-structured toroidal type continuously variable transmission is in use, if the cam plate 10 is rotated with the rotation of the input shaft 1,,then the plurality of rollers 12, 12 are pressed against the cam surface 14 on the outer surface of the input-side disk 2 by the cam surface 13. As a result of this, the input-side disk 2 is pressed against the plurality of power rollers 8, 8 and, at the same time, the pair of cam surfaces 13 and 14 are pressed against the plurality of rollers 12, 12, so that the input-side disk 2 is rotated. And, the rotation of the input-side disk 2 is transmitted through the plurality of power rollers 8, 8 to the output-side disk 4, so that the output shaft 3 fixed to the output-side disk 4 is rotated.
In a case of changing the rotation speed of the input and output shafts 1 and 3, in particular, at first, when decelerating the rotation speed between the input and output shafts 1 and 3, the trunnions 6, 6 are respectively swung about the pivots 5, 5, and the displacement shafts 7, 7 are respectively inclined so that the peripheral surfaces 8a, 8a of the power rollers 8, 8, as shown in FIG. 1, can be respectively contacted with the portion of the inner surface 2a of the input-side disk 2 located near the center thereof and with the portion of the inner surface 4a of the output-side disk 4 located near the outer periphery thereof.
Also, on the other hand, when accelerating the rotation speed between the input and output shafts 1 and 3, the trunnions 6, 6 are respectively swung about the pivots 5, 5, and the displacement shafts 7, 7 are respectively inclined so that the peripheral surfaces 8a, 8a of the power rollers 8, 8, as shown in FIG. 2, can be respectively contacted with the portion of the inner surface 2a of the input-side disk 2 located near the outer periphery thereof and with the portion of the inner surface 4a of the output-side disk 4 located near the center thereof. By the way, if the inclination angle of the displacement shafts 7, 7 is set in the middle of the inclination angles shown in FIGS. 1 and 2, then there can be obtained an intermediate transmission ratio between the input and output shafts 1 and 3.
Now, FIG. 3 shows a more specified toroidal type continuously variable transmission which is disclosed in U.S. Pat. No. 4,955,246. As shown in FIG. 3, an input-side disk 2 and an output-side disk 4 are rotatably supported on the periphery of a cylindrical input shaft 15 respectively through needle bearings 16 and 16.
Also, a cam plate 10 is spline engaged with the outer peripheral surface of the end portion (in FIG. 3, the left end portion) of the input shaft 15 and is prevented, by a flange portion 17, from moving in a direction away from the input-side disk 2. Further, the cam plate 10 cooperates together with rollers 12 and 12 in forming a pressure device 9 of a loading cam type.
The pressure device 9, in accordance with the rotation of the input shaft 15, rotates the input-side disk 2 while it is pressing against the input-side disk 2 toward the output-side disk 4. An output gear 18 is connected to the output-side disk 4 by keys 19 and 19, so that the output-side disk 4 and output gear 18 can be rotated synchronously with each other.
A pair of trunnions 6 and 6, in particular, their respective two end portions thereof are supported on a pair of support plates (not shown) in such a manner that they can be swung and can be displaced in the axial direction (in FIG. 1 in the front and back direction) thereof. And, two displacement shafts 7 and 7 are respectively supported in circular holes (not shown) portions which are respectively formed in the middle portions of the pair of trunnions 6 and 6. The two displacement shafts 7 and 7 respectively include support shaft portions 21, 21 and pivot shaft portions 22, 22 which are extend in parallel to each other but are eccentric to each other. The support shaft portions 21 and 21 are rotatably supported inside the circular holes through needle bearings (not shown), respectively. Also, power rollers 8 and 8 are rotatably supported in the peripheries of the pivotal shaft portions 22 and 22 through another needle bearings 25 and 25, respectively.
By the way, the pair of displacement shafts 7 and 7 are respectively located on 180 deg.-separated opposite sides with respect to the input shaft 15. Also, a direction, -in which the pivot shaft portions 22 and 22 of the displacement shafts 7 and 7 are eccentric to the support shaft portions 21 and 21, is set as the same direction with respect to the rotation direction of the input- and output-side disks 2 and 4. Also, the eccentric direction is set almost at right angles to the direction in which the output shaft is disposed. Therefore, the power rollers 8 and 8 are supported in such a manner that they can be somewhat displaced in the disposing direction of the input shaft 15. As a result of this, even when the power rollers 8 and 8 are displaced in the axial direction of the input shaft 15 owing to the dimensional precision of the components, elastic deformation thereof and the like, the displaced conditions of the power rollers 8 and 8 can be absorbed without applying excessive forces to the components.
Also, between the outer surfaces of the power rollers 8, 8 and the inner surfaces of the middle portions of the two trunnions 6, 6, there are interposed thrust ball bearings 26, 26 and thrust needle bearings 27, 27. The thrust ball bearings 26 and 26 are respectively used to allow the power rollers 8 and 8 to rotate while supporting the loads applied to the power rollers 8 and 8 in the thrust direction. The thrust ball bearings 26 and 26 are respectively composed of a plurality of balls 29, 29, - - - , annular-shaped retainers 28, 28 for retaining the balls 29, 29 in a freely rollable manner, and annular-shaped outer races 30, 30. The inner raceways of the thrust ball bearings 26, 26 are respectively formed on the outer surfaces of the two power rollers 8, 8, whereas the outer raceways thereof are respectively formed on the inner surfaces of the outer rings 30, 30.
The thrust needle bearings 27 and 27 are respectively composed of races 31, retainers 32 and needle rollers 33, 33. The races 31 and retainers 32 (see FIG. 9) are combined together in such a manner that they can be somewhat displaced in the rotation direction. Also, the races 31 and retainers 32 respectively include annular portions (not shown) with the pivot shaft portions 22 as the centers thereof, and projecting portions (not shown) which respectively project from the partial outer peripheral edges of their associated circular portions outwardly in the diameter direction thereof.
Now, FIGS. 4 and 5 are respectively inner surface views of a trunnion to which a thrust needle bearing according to the invention set forth in U.S. Pat. No. 5,720,689 is assembled. In particular, FIG. 4 shows a neutral state of the trunnion and FIG. 5 shows the maximum displaced state thereof. The present invention is characterized in that, in order to prevent needle rollers 33, 33 forming a thrust needle bearing 27c from protruding from a race 31B which is so disposed on the inner surface of a trunnion 6 as not to protrude from this inner surface of the trunnion 6, there is formed an uneven-shaped securing portion (which is composed of a projecting portion 54 and a recessed portion 56) between the retainer 48 and trunnion 6.
The retainer 48 can be produced by forming a plurality of rectangular-shaped pockets 41, 41, - - - , in a base plate 49 made of a metal plate, synthetic resin plate, or the like. Also, in a portion of the base plate 49 which is shifted to one side in the longitudinal direction thereof from the center thereof, there are formed a circular hole 50 and a cutaway portion 51 which projects from part of the circular hole 50 outwardly in the diameter direction thereof. A projecting member 52, which is formed on the inner surface of the trunnion 51, is rotatably fitted into the circular hole 50 with no play between them.
In the trunnion 6, there is formed another circular hole 23 through which the support shaft portion 21 of the displacement shaft 7 can be inserted, while one end of the circular hole 23 is open to the inside of the projecting member 52. In a state where the circular hole 50 is fitted over the projecting member 52, the longitudinal direction of the respective pocket holes (roller grooves) 41 formed in the base plate 49 of the retainer 48 is consistent with a radial direction with the circular hole 50 as the center thereof. Therefore, the axial direction of all the needle rollers 33 forming the thrust needle bearing 27c is consistent with a radial direction the center of which is the support shaft portion 21 that is inserted into the circular hole 23. By the way, in FIGS. 4 and 5, reference characters 55a and 55b respectively designate folded portions.
However, in the above-mentioned related continuously variable transmission, the retainer 48, similarly to an ordinary thrust needle bearing, has a thickness of the order of 0.5 mm and thus it cannot satisfy the required conditions on the hardness and hardened layer depth to a satisfactory degree; and, therefore, as shown in FIG. 6, there can be caused a crack 42 in the portion of the retainer 48 that is the center portion side between the roller grooves 41, 41 into which the needle rollers 33, 33 can be inserted.
In this connection, to increase the capacity for the thrust load, the number of needle rollers must be increased; and, if the number of needle rollers is increased, then the width t (see FIG. 7C) of a retainer pillar between the roller grooves is decreased and thus the strength thereof is lowered. Also, if the width t is excessively small, then it is impossible to manufacture the retainer 48 by press working.